This invention relates to medical diagnostic ultrasound imaging, and in particular to the real-time acquisition of 3-D ultrasound images.
Real-time 3-D ultrasound image acquisition relies on two-dimensional (2-D) transducer arrays to acquire ultrasound image data over a 3-D imaged volume in real-time.
The two-way transmit time for the acoustic pulse is the fundamental frame rate limiting parameter in ultrasound imaging. The problem of low frame rate becomes severe in three-dimensional real-time imaging. If the maximum imaging depth is 150 millimeters and the application requires 20 frames per second, then there are a maximum of about 256 transmit events per frame. The standard response to this problem is to use multiple receive lines per transmit event to achieve a higher spatial sampling rate.
One prior-art system marketed by Volumetrics uses a 16.times.16 transmit line firing pattern. A 4.times.4 receive line reception pattern is acquired for each transmit firing. This results in coarse sampling that has an adverse impact on image quality and that fundamentally limits resolution. The Volumetrics system currently operates with a 65.degree. pyramid, rather than the 90.degree. pyramid which is often preferred. The reduced field of view is at least partially used in order to improve frame rate, but a 65.degree. pyramid is inherently limited in terms of clinical utility. When looking at a 2-D slice through the acquired 3-D volume, the approach taken by the Volumetrics system is equivalent to having used only 16 transmit beams and 16.times.4 (64) receive beams for each 2-D slice.